1. Field of the Invention
The present invention relates to a motor driven bell for producing a sound of a bell (sounding a bell) in a manner that a hammer member hits a gong through the use of driving force of a motor.
2. Description of the Related Art
FIGS. 7 and 8 are cross-sectional views showing a motor driven bell disclosed in the Japanese Utility Model Publication No. H3-69199.
In the illustrations, numeral 31 represents a gong, and numeral 32 designates a hammer member fixed at right angles to a portion adjacent to a tip portion 33a of a plate spring 33. Further, numeral 34 denotes a support for fixing the proximal portion of the plate spring 33, with the plate spring 33 being held at right angles with respect to a drive shaft 36 of a motor 35. The tip portion 33a of the plate spring 33 is inclined with respect to the drive shaft 36 of the motor 35 to further separate from a circumferential wall 31a of the gong 31 as it becomes closer to its tip, and a cam member 37 is formed to have a disc-like configuration and is supported by the motor shaft 36 in a state of being in an eccentric condition. Besides, the aforesaid tip portion 33a is located to face the interior of the locus of a circumferential portion 37a of a large-diameter section of the cam member 37. With this arrangement, when the motor 35 is driven in the FIG. 7 state to rotate the cam member 37, the circumferential portion 37a of its large-diameter section gradually approaches the tip portion 33a of the plate spring 33 so that as shown in FIG. 8 the circumferential portion 37a of the large-diameter section finally comes into contact with the tip portion 33a of the plate spring 33 to push the tip portion 33a of the plate spring 33 toward its proximal portion 33b. At this time, since the tip portion 33a is in the inclined condition with respect to the drive shaft 36, the force of pushing toward the proximal portion 33b is converted into a force to be applied in a direction of separating from a circumferential wall 31a of the gong 31, so that the plate spring 33 is deflected in a direction of separating from the gong 31 in a state where the aforesaid proximal portion 33b works as a supporting point and the hammer member 32 separates from the circumferential wall 31a of the gong 31, while a returning force F occurs in the plate spring 33. Thereafter, as the cam member 37 further rotates to cause the cam member 37 to disconnect from the tip portion 33a of the plate spring 33 as shown in FIG. 7, the plate spring 33 returns to the snap condition due to its own returning force F so that the hammer member 32 hits the gong 31 to ring a bell.
With the arrangement mentioned above, in the prior motor driven bell, the abrasion of the cam member and the plate spring is little because the cam member intermittently comes into contact with the plate spring, but on the other hand there are problems such that the power consumption increases because the cam member necessarily once comes into contact with the plate spring per one revolution of the drive shaft and slides against the repulsion of the plate spring, and further that the natural frequency of the plate spring differs from the frequency of the plate spring occurring when being forcibly moved by the cam member, causing the plate spring and the cam member to act against each other to offset the hitting force of the hammer member to the gong.